Putting up a fence, does post need concreted in or not?

Question

The installer says I should, but my uncle says that concrete causes the wood to rot faster. Not sure which way to go.

Answer 1

Concrete serves two functions: resisting compression loads (weight put on top of it) and as dead weight (adding mass to metal fence posts, for example). Your situation requires neither.

A wood post is best supported by using the excavated material. Set the posts 3' deep (or below frost line in really cold climates, whichever is deeper). Put 4-6" pea gravel in the bottom of each hole to keep the posts off the dirt. Backfill holes 8-12" at a time and tamp with a tamping bar. This is a 40 lb bar that has a 3" blade on one end (for 'mixing' Sakrete in a hole), and looks like a nail head on the other end (for tamping dirt around posts). You'll use the nail head looking end. They cost about $20 and are 5-6' long.

The reason the dirt is better than concrete is b/c most pressure treated lumber has a very high moisture content from the lumber yard. I've gotten squirted in the eye with water from hitting a board with a hammer. As the wood dries, it shrinks. The concrete wont shrink with it, leaving the wood just standing in a square hole in the concrete. I've had to fix several handrails with this problem. I just lifted the posts right out of the concrete, removed the blocks, and replaced them with longer posts backfilled with dirt.

As for rotting, pressure treated lumber does rot. It is only resistant to rot, not impervious. Concrete holds moisture, which will wick up into the post. The post won't rot in the conventional sense, like being eaten by bugs and such, but it will get spongey. Exposure to constant moisture will cause the arsenic to leech out of the wood and it will be attacked by microorganisms. That's why those tiny labels on the ends of the boards say not to use them underwater or in contact with constant moisture.

Bottom line; use dirt. Concrete is for putting weight on top of, like a footer, or for making those metal posts that they use in chain link fences bottom heavy. It should never be used to anchor a wooden post. Using dirt means that the posts can always be fixed in place if they lean or fail. Concrete is a one-shot deal.

Whenever you do any kind of construction, you have to be able to explain to someone else WHY you're doing it the way that you are and why you're NOT doing it some other way. If someone tells you, "that's the way we always do it", or "it's just better that way" and can't explain in detail why, then they don't know what they are doing. It is more important to understand a process than it is to 'know how to do it'.

Answer 2

Fence Posts Without Concrete

Answer 3

All of your answers to date point out the exact problem with your question. The answer is..... It depends. You need to take into consideration the soils type and bearing capacity of that soil, the temperature ranges for your area, ie; freezing winters in Maine VS no freeze at all in Texas, plus the design, layout of the fence, the height, and spacing of structural posts. Then, once all that is in the equation, further refine your design info to include depth of hole, size of post, and size of the hole circumference.

It is generally accepted that a four foot depth of hole with a concrete base 2 1/2 times the circumference of the post, and rising up the post only 1/2 the depth of the hole, will provide optimum support for the post given the design criteria in frost affected ares. In non frost areas, I'm just not sure what the recommendations would be. Best to check with the local codes office, the building materials store, or a structural engineer.

It is also imperative to use the proper post. Even pressure treated lumber has different ratings for above grade, below grade, and submerged water contact for their pressure treating process. So an above grade post installed in a hole in the ground that can collect water in it will rot over time, even though it's pressure treated. Only pressure treated and Cedar posts are recommended, but the Cedar WILL rot over time, again depending on water table, freeze, and rain exposure. Let me know how you make out. Good luck

Answer 4

no.
tamping the post back in with the excavated material is fine. Concrete is overkill and a tad pricey if the fence is long, unless of course its in a place where it will take substainial abuse.....as in holding cattle. When you tamp (take a long pole and pack in the excavated material) you may run short, its best to mix a little sand in with it. so its about 50/50 sand/clay mix. If you are in a sandy area, you can get bag drymix (its much cheaper than conc.). Pour the dry mix in the hole, tamp it good so the post is secure (1 bag per hole, hole should be min 3' deep) and fill the rest of the hole with excated material, Afterwards water the holes....the drymix will turn into a kind of concrete,also will suck moisture right out of the ground. Works well in poor soil conditions. Make sure you are using treated or cedar posts....nothing else is acceptable, everything else will rot out.

Answer 5

I try to make it short and sweet.

Wood expands and contracts way more than concrete.

Summer months wood dries out leaving a gap between concrete,Rains come run down post and are trapped within the void in concrete. You just built a swimming pool for your post.

You can use redwood, pressure treat to no availe.

Tamp your post with a product that will allow proper drainage.

Answer 6

It does not make it rot faster it would be fine. However depending on the fence and how much of a wind beating you probably don't need concrete, if it is going to take alot of abuse then use concrete. Take a look at the posts on someones wood deck and you will see concrete piers for it.

Answer 7

There are different ways of doing it yes you should use concrete.You can use a pvc pipe big enough to fit the posts in and surround the post with concrete in it.This no doubt would be all underground .Not using concrete to help anchor the post actually makes them rot faster and is not a stable means of support.

Answer 8

I would not use concrete-you can buy metal fence posts-if they rise up in winter or any time you can just pound them back down. They work great.

Answer 9

You don't always need to use concrete to secure fence posts in to the ground. Sometimes, depending on the post, you can simply drive it deep into the ground. Using a tools called a post rammer like this one http://www.avsfencing.co.uk/fencing/accessories/tools/115mm-post-rammer/ This will make it easier to drive the post in.

Answer 10

We installed a very long privacy fence around our backyard. We cemented in the corner posts and all of the rest were filled with pea rock around the treated post. We have a lot of wind here and the fence moves with the wind.